1. Field of the Invention
The present invention relates to the technical field of trailer system, more particularly, to a reversible plate positioning device for a stationary radiation imaging trailer system.
2. Description of the Related Art
Stationary radiation imaging inspection system is commonly employed for Customs, civil airports and railway systems etc. Generally, the radiation imaging inspection system is provided with a stationary radiation source and an array detector for receiving rays that penetrate through a vehicle to be detected in a detection passage that can shield rays. A specific trailing device detects a vehicle carrying a container with ray beams. The rays penetrating through the container is transmitted to the detector which reflects density distribution of items in the container based on the variation of the ray intensity, and the ray intensity is transformed into image gray scale, thus obtaining the perspective images of the objects in the container.
In the prior art, the specific trailing device is generally configured to be a platform lorry or a plate-link-chain conveyer. For example, a 2000 series container/vehicle detection system manufactured by Rapiscan Inc. employs a platform lorry. The whole truck carrying the container is driven onto the platform lorry which carries the truck through the rays. However, the platform lorry occupies a large area and is at high cost. As the vehicle to be detected can not be reliably positioned and the operation of the system is not stable, high image quality can not be achieved. In addition, the vehicle to be detected can not easily be uploaded since the distance between the platform lorry and the floor is relatively large. And the polygon effect of plate-link-chain transmission degrades the quality of image, and the noise thereof is unbearable. Applicant's Chinese Patent No. 02148669.7 (Publication number CN1500685) entitled “trailer for automated scanning radiation inspecting system of large object” sought to overcome the aforementioned disadvantages of prior art. Based upon the aforementioned patent, the applicant filed Chinese Patent Application No. 200310100183.6 (Publication number CN1607122) entitled “trailer system for radiation imaging” and Chinese Patent Application No. 200310100184.0 (Publication number CN1607135) entitled “trailer of trailer system for radiation imaging” on Oct. 16, 2003 respectively. The trailer of the above inventions has the advantages of low noise, less occupancy area and low cost etc. respectively. Furthermore, the stability of operation of the system is enhanced, and the platform of the vehicle body is lowered for convenience of the upload of the vehicle to be detected. In addition, a wheel positioning and trailer body anchoring device is provided. However, the aforementioned techniques still have the following disadvantages:
When the vehicle to be detected is downloaded, all wheels except front ones of the vehicle would run over a crank plate with a normally lifted-up upper end face in a wheel-locking device. As a result, the trailer and the wheels of the vehicle to be detected both generates impact force during the unloading of the vehicle to be detected, resulting in instability of unloading operation of the vehicle to be detected.